Epoxy resins have many desirable properties which make them attractive as coatings, adhesives, paper release agents, additives for printing inks, and for other applications. Included among these desirable properties are low viscosity, excellent clarity, high gloss, and high reactivity.
Additionally, epoxy resins have variable UV cure rates as measured by a PPG UV Processor. For example, 3,4-epoxycylcohexyl-methyl-3',4'-epoxycyclohexane carboxylate, a typical highly reactive cycloaliphatic epoxide obtained from Ciba-Gigy as "CY-179"; cures at a rate of 40 ft./min. under two 300 W UV lamps in the presence of 0.5 mole % (4-octyloxyphenyl)phenyliodonium hexafluoroantimonate.
E. P. Plueddemann and G. Fanger, J. Am. Chem. Soc., vol. 81, p. 2632, 1959, describe the preparation of a number of silicon-containing epoxy monomers by hydrosilation of silicon hydrides and vinyl functional epoxides. Two of these epoxy monomers, which consist of short siloxane chains of two units terminated by cycloaliphatic epoxy groups, exhibit extraordinary reactivity when UV cured in the presence of diaryliodonium salts. The UV cure rates measured for these compounds are greater than 500 ft/min using a single 300 W UV lamp in the presence of 0.5 mole % (4-octyloxyphenyl)phenyliodonium hexafluoroantimonate.
It would be advantageous to develop different epoxy functional siloxane monomers based on a cyclic siloxane structure. Among the advantages are low initial viscosity, low toxicity, and high reactivity. Until now, however, cyclic epoxy-functional siloxanes have not been produced because side reactions caused premature crosslinking and the formation of gels.
U.S. Pat. Nos. 4,219,654 (Crivello); 4,026,705 (Crivello et al.); and 4,417,061 (Crivello) describe the use of diaryliodonium and trialylsulfonium salts as efficient photoinitiators in the cationic polymerization of epoxy resins and monomers. Included among the epoxy resins and monomers are polydimethylsiloxane resins having pendant and terminal glycidyl ether groups. The problem with resins which contain both pendant and terminal epoxy functional groups, however, is that, since they are polymeric, their viscosity is relatively high as compared to low molecular weight resins which contain only terminal epoxy functional groups. This limits their utility in coating and other applications where low viscosity compositions are required.
It is an object of this invention, therefore, to produce novel cyclic epoxy functional silicone monomers which have low initial viscosity yet are highly reactive in cationic photo-initiated polymerization reactions.
It is further an object of this invention to determine a method of producing cyclic epoxy functional silicone monomers which have low initial viscosity yet are highly reactive in cationic photoinitiated polymerization reactions.
Still further it is an object of this invention to produce an epoxy functional siloxane monomer that has low toxicity.